There are a number of applications in which so-called "air knives" are used to clean workpieces, such devices having means for directing a stream of air so as to remove an unwanted deposit from a portion of a workpiece. Air knives find particular application in powder coating systems, wherein particulate materials are deposited, with or without the aid of electrostatic effects, upon the workpiece. While various masking techniques are widely used in such systems, often they are either not sufficiently effective or precise to maintain the uncoated parts as powder-free as may be necessary, or subsequent transfer of the powder from the coated to the uncoated areas causes intolerable contamination of the latter. Normally, air knives are used to clean the parts prior to conversion of the particulate material to a permanent coating.
Typically, air knives have, in the past, taken the form of a series of discrete nozzles or needles disposed at spaced locations along the travel path of a conveyed workpiece. While effective for many purposes, it has been found that separate nozzles are rather unsatisfactory for the cleaning of thin or fine parts, such as the wire leads of electrical components. The surges of air to which the part is subjected in passing from one of such nozzles to the next produces imprecise definition between the coated and uncoated areas, and causes particles to be dislodged from the areas on which a coating is necessary. Also, some difficulty is experienced in setting-up and adjusting a series of individual nozzles, and in maintaining them in proper order to produce optimum results.
Accordingly, it is an object of the present invention to provide a novel cleaning system utilizing air knife apparatus which is capable of producing a uniform sheet or stream of air, which system may be used to produce a precise margin between coated and uncoated portions of workpieces conveyed therethrough.
It is also an object of the invention to provide such a system, whch is efectively employed for cleaning thin and fine parts without causing undesirable air surge effects.
Another object is to provide such a system, which is simple and economical to construct, and facile to use and maintain.